Force sensing with an electromagnetic load

ABSTRACT

A system for performing force sensing with an electromagnetic load may include a signal generator configured to generate a signal for driving an electromagnetic load and a processing subsystem configured to monitor at least one operating parameter of the electromagnetic load and determine a force applied to the electromagnetic load based on a variation of the at least one operating parameter.

RELATED APPLICATIONS

The present disclosure claims priority to U.S. Provisional PatentApplication Ser. No. 62/826,327, filed Mar. 29, 2019, which isincorporated by reference herein in its entirety.

The present disclosure is also related to U.S. patent application Ser.No. 16/556,849, filed Aug. 30, 2019 (“Tracking Application 1”), U.S.patent application Ser. No. 16/556,897, filed Aug. 30, 2019 (“TrackingApplication 2”), and U.S. patent application Ser. No. 16/559,238, filedSep. 3, 2019 (“Tracking Application 3”, and together with TrackingApplication 1 and Tracking Application 2, the “Tracking Applications”),each of which is incorporated by reference herein in its entirety.

FIELD OF DISCLOSURE

The present disclosure relates in general to tracking a resonantfrequency of a transducer, for example a haptic transducer, and drivingsuch transducer at or near its resonant frequency.

BACKGROUND

Vibro-haptic transducers, for example linear resonant actuators (LRAs),are widely used in portable devices such as mobile phones to generatevibrational feedback to a user. Vibro-haptic feedback in various formscreates different feelings of touch to a user's skin, and may playincreasing roles in human-machine interactions for modern devices.

An LRA may be modelled as a mass-spring electro-mechanical vibrationsystem. When driven with appropriately designed or controlled drivingsignals, an LRA may generate certain desired forms of vibrations. Forexample, a sharp and clear-cut vibration pattern on a user's finger maybe used to create a sensation that mimics a mechanical button click.This clear-cut vibration may then be used as a virtual switch to replacemechanical buttons.

FIG. 1 illustrates an example of a vibro-haptic system in a device 100.Device 100 may comprise a controller 101 configured to control a signalapplied to an amplifier 102. Amplifier 102 may then drive a vibrationalactuator (e.g., haptic transducer) 103 based on the signal. Controller101 may be triggered by a trigger to output to the signal. The triggermay for example comprise a pressure or force sensor on a screen orvirtual button of device 100.

Among the various forms of vibro-haptic feedback, tonal vibrations ofsustained duration may play an important role to notify the user of thedevice of certain predefined events, such as incoming calls or messages,emergency alerts, and timer warnings, etc. In order to generate tonalvibration notifications efficiently, it may be desirable to operate thehaptic actuator at its resonance frequency.

The resonance frequency f₀ of a haptic transducer may be approximatelyestimated as:

$\begin{matrix}{f_{0} = \frac{1}{2\pi\sqrt{CM}}} & (1)\end{matrix}$where C is the compliance of the spring system, and M is the equivalentmoving mass, which may be determined based on both the actual movingpart in the haptic transducer and the mass of the portable deviceholding the haptic transducer.

Due to sample-to-sample variations in individual haptic transducers,mobile device assembly variations, temporal component changes caused byaging, and use conditions such as various different strengths of a usergripping of the device, the vibration resonance of the haptic transducermay vary from time to time.

FIG. 2 illustrates an example of a linear resonant actuator (LRA)modelled as a linear system. LRAs are non-linear components that maybehave differently depending on, for example, the voltage levelsapplied, the operating temperature, and the frequency of operation.However, these components may be modelled as linear components withincertain conditions. In this example, the LRA is modelled as a thirdorder system having electrical and mechanical elements. In particular,Re and Le are the DC resistance and coil inductance of the coil-magnetsystem, respectively; and Bl is the magnetic force factor of the coil.The driving amplifier outputs the voltage waveform V(t) with the outputimpedance Ro. The terminal voltage V_(T)(t) may be sensed across theterminals of the haptic transducer. The mass-spring system 201 moveswith velocity u(t).

SUMMARY

In accordance with the teachings of the present disclosure, thedisadvantages and problems associated with existing approaches forsensing application of force in a host device may be reduced oreliminated.

In accordance with embodiments of the present disclosure, a system forperforming force sensing with an electromagnetic load may include asignal generator configured to generate a signal for driving anelectromagnetic load and a processing subsystem configured to monitor atleast one operating parameter of the electromagnetic load and determinea force applied to the electromagnetic load based on a variation of theat least one operating parameter.

In accordance with these and other embodiments of the presentdisclosure, a method for performing force sensing with anelectromagnetic load may include generating a signal for driving anelectromagnetic load, monitoring at least one operating parameter of theelectromagnetic load, and determining a force applied to theelectromagnetic load based on a variation of the at least one operatingparameter.

Technical advantages of the present disclosure may be readily apparentto one having ordinary skill in the art from the figures, descriptionand claims included herein. The objects and advantages of theembodiments will be realized and achieved at least by the elements,features, and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are examples and explanatory and arenot restrictive of the claims set forth in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 illustrates an example of a vibro-haptic system in a device, asis known in the art;

FIG. 2 illustrates an example of a Linear Resonant Actuator (LRA)modelled as a linear system, as is known in the art; and

FIG. 3 illustrates selected components of an example host deviceincorporating force sensing using an electromagnetic load of the hostdevice, in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

The description below sets forth example embodiments according to thisdisclosure. Further example embodiments and implementations will beapparent to those having ordinary skill in the art. Further, thosehaving ordinary skill in the art will recognize that various equivalenttechniques may be applied in lieu of, or in conjunction with, theembodiment discussed below, and all such equivalents should be deemed asbeing encompassed by the present disclosure.

Various electronic devices or smart devices may have transducers,speakers, and acoustic output transducers, for example any transducerfor converting a suitable electrical driving signal into an acousticoutput such as a sonic pressure wave or mechanical vibration. Forexample, many electronic devices may include one or more speakers orloudspeakers for sound generation, for example, for playback of audiocontent, voice communications and/or for providing audiblenotifications.

Such speakers or loudspeakers may comprise an electromagnetic actuator,for example a voice coil motor, which is mechanically coupled to aflexible diaphragm, for example a conventional loudspeaker cone, orwhich is mechanically coupled to a surface of a device, for example theglass screen of a mobile device. Some electronic devices may alsoinclude acoustic output transducers capable of generating ultrasonicwaves, for example for use in proximity detection type applicationsand/or machine-to-machine communication.

Many electronic devices may additionally or alternatively include morespecialized acoustic output transducers, for example, haptictransducers, tailored for generating vibrations for haptic controlfeedback or notifications to a user. Additionally or alternatively, anelectronic device may have a connector, e.g., a socket, for making aremovable mating connection with a corresponding connector of anaccessory apparatus, and may be arranged to provide a driving signal tothe connector so as to drive a transducer, of one or more of the typesmentioned above, of the accessory apparatus when connected. Such anelectronic device will thus comprise driving circuitry for driving thetransducer of the host device or connected accessory with a suitabledriving signal. For acoustic or haptic transducers, the driving signalmay generally be an analog time varying voltage signal, for example, atime varying waveform.

FIG. 3 illustrates selected components of an example host device 300incorporating force sensing using an electromagnetic load 301 of hostdevice 300, in accordance with embodiments of the present disclosure.Host device 300 may include, without limitation, a mobile device, homeapplication, a vehicle, and/or any other system, device, or apparatusthat includes a human-machine interface. Electromagnetic load 301 mayinclude any suitable load with a complex impedance, including withoutlimitation a haptic transducer, a loudspeaker, a microspeaker, apiezoelectric transducer, or other suitable transducer.

In operation, a signal generator 324 of a processing subsystem 305 ofhost device 300 may generate a signal x(t) (which, in some embodiments,may be a waveform signal, such as a haptic waveform signal or audiosignal). Signal x(t) may in turn be amplified by amplifier 306 togenerate the driving signal V(t) for driving electromagnetic load 301.Responsive to driving signal V(t), a sensed terminal voltage V_(T)(t) ofelectromagnetic load 301 may be converted to a digital representation bya first analog-to-digital converter (ADC) 303. Similarly, sensed currentl(t) may be converted to a digital representation by a second ADC 304.Current l(t) may be sensed across a shunt resistor 302 having resistanceR_(s) coupled to a terminal of electromagnetic load 301. The terminalvoltage V_(T)(t) may be sensed by a terminal voltage sensing block 307,for example a volt meter.

As shown in FIG. 3 , processing subsystem 305 may include a back-EMFestimate block 308 that may estimate back-EMF voltage V_(B)(t). Ingeneral, back EMF voltage V_(B)(t) may not be directly measured fromoutside of the haptic transducer. However, the terminal voltage V_(T)(t)measured at the terminals of the haptic transducer may be related toV_(B)(t) by:

$\begin{matrix}{{V_{T}(t)} = {{V_{B}(t)} + {{Re} \cdot {I(t)}} + {{Le} \cdot \frac{{dI}(t)}{dt}}}} & (2)\end{matrix}$where the parameters are defined as described with reference to FIG. 2 .Consequently, back-EMF voltage V_(B)(t) may be estimated according toequation (2) which may be rearranged as:

$\begin{matrix}{{V_{B}(r)} = {{V_{T}(r)} - {{Re} \cdot {I(t)}} - {{Le}\frac{{dI}(t)}{dt}}}} & (3)\end{matrix}$

In some embodiments, back-EMF estimate block 308 may be implemented as adigital filter with a proportional and parallel difference path. Theestimates of DC resistance Re and inductance Le may not need to beaccurate (e.g., within an approximate 10% error may be acceptable), andthus, fixed values from an offline calibration or from a data sheetspecification may be sufficient. As an example, in some embodiments,back-EMF estimate block 308 may determine estimated back-EMF voltageV_(B)(t) in accordance with the teachings of Tracking Application 3.

Also as depicted in FIG. 3 , processing subsystem 305 may include aresonant frequency detector 310 configured to estimate a resonancefrequency f₀ of electromagnetic load 301. As shown, resonant frequencydetector 310 may be configured to estimate resonance frequency f₀ basedon sensed current l(t) and estimated back-EMF voltage V_(B)(t) using oneor more of the techniques described in the Tracking Applications.However, in some embodiments, one or more other measured quantitiesassociated with electromagnetic load 301 may be used to determine itsresonance frequency f₀.

A parameter monitor 312 of processing subsystem 305 may receive signalsindicative of one or more of resonance frequency f₀, sensed currentl(t), terminal voltage V_(T)(t), and estimated back-EMF voltageV_(B)(t), and based on one or more of such parameters, determine whethera force has been applied (e.g., by a user of host device 300) toelectromagnetic load 301. Based on such detected force, a processor 314of processing subsystem 305 may take one or more responsive actions asdescribed in greater detail below.

In some embodiments, the determination of whether a force has beenapplied may be based on other parameters derived from one or more ofresonance frequency f₀, sensed current l(t), terminal voltage V_(T)(t),and estimated back-EMF voltage V_(B)(t), such as, for example, a compleximpedance of electromagnetic load 301 (or change to such compleximpedance) and/or a quality factor (or change to such quality factors)may be estimated from sensed current l(t), terminal voltage V_(T)(t),and/or estimated back-EMF voltage V_(B)(t) as described in TrackingApplication 2 and Tracking Application 3.

To further illustrate, in response to driving signal V(t) beingreproduced at electromagnetic load 301 (e.g., a haptic effect, playbackof sounds, etc.), a user may grip or otherwise apply force to hostdevice 300. For example, a haptic effect and/or playback of sounds(e.g., a ringtone) may provide to a user an indication of an incomingphone call, text message, electronic mail, or other electroniccommunication. A force applied by the user upon electromagnetic load 301(e.g., either directly or indirectly by force applied to an enclosure ofhost device 300) may lead to a shift in one or more parameters (e.g.,resonance frequency f₀, impedance) of electromagnetic load 301. Thus,processing subsystem 305 may monitor such one or more parameters,determine based on such one or more parameters whether a force has beenapplied on electromagnetic load 301, and undertake a responsive actionif force is detected.

Accordingly, electromagnetic load 301 may simultaneously act as anoutput transducer/actuator in addition to an input force sensor, inwhich a change in gripping force applied to host device 300 is detectedas a change in one or more operating parameters (e.g., impedance,resonance frequency f₀, sensed current l(t), terminal voltage V_(T)(t),estimated back-EMF voltage V_(B)(t), complex impedance, quality factor,and/or another parameter) of electromagnetic load 301. The magnitude ofchange of the one or more operating parameters may provide an indicationof a magnitude of force (or change of force) applied to host device 300.Thus, processing subsystem 305 may apply one or more thresholds to thechange in the one or more operating parameters (e.g., a change of 1%-2%of the magnitude of the operating parameters). For example, if anoperating parameter in interest changes by less than a thresholdpercentage, parameter monitor 312 may not even process such change as anapplication of force. However, if the operating parameter in interestchanges by more than the threshold percentage, parameter monitor 312 mayprocess such change as an application of force, and take an appropriateresponse action. In some embodiments, a second threshold (or additionalthresholds) may be present, such that changes in an operating parameterbeyond such additional thresholds may lead to other response actions.

Although the foregoing contemplates detection of a force event inresponse to a change in one or more operating parameters, in someembodiments, more sophisticated approaches may be used to detect forceevents. For example, in some embodiments, a machine learning classifiersuch as a Support Vector Machine (SVM), Convolutional Neural Network(CNN), and/or classifier may be used to extract features of one or moreoperation parameter changes corresponding to force events and from suchchanges determine what type of force event has occurred.

As mentioned, based on a presence and/or magnitude of force applied tohost device 300 as sensed by electromagnetic load 301, processor 314 mayprovide one or more responsive actions in response to the applied force.For example, in some embodiments, such one or more responsive actionsmay include altering signal x(t) responsive to force, thus modifying ahaptic effect generated by electromagnetic load 301 (e.g., whenelectromagnetic load 301 comprises a vibrational actuator). As aspecific example, the haptic effect a user perceives may vary based onhow firmly the user grips a host device. In order to create a steadyhaptic effect to a user, it may be desirable to reduce a responsivehaptic effect as detected grip force increases. As another example, inthese and other embodiments, such one or more responsive actions mayinclude processor 314 causing one or more user interface events to occurat a display device (not explicitly shown) of host device 300 (e.g., viathe interaction of processor altering signal x(t)) responsive to force.As a further example, in these and other embodiments, such one or moreresponsive actions may include performing health diagnostics responsiveto force (e.g., force, including a reaction time in applying the force,may be indicative of motor reflex of the user).

The use of an electromagnetic load 301 as an input force sensor may havemany advantages. For example, such use may avoid a need for somemechanical and/or other dedicated force sensing buttons on host device300. In addition, such use may provide another user mode of interactionwith host device 300 that does not require access to a screen, touchsensor, microphone, or other external mechanical device.

As used herein, when two or more elements are referred to as “coupled”to one another, such term indicates that such two or more elements arein electronic communication or mechanical communication, as applicable,whether connected indirectly or directly, with or without interveningelements.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the example embodiments herein that aperson having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, or component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative. Accordingly, modifications, additions, oromissions may be made to the systems, apparatuses, and methods describedherein without departing from the scope of the disclosure. For example,the components of the systems and apparatuses may be integrated orseparated. Moreover, the operations of the systems and apparatusesdisclosed herein may be performed by more, fewer, or other componentsand the methods described may include more, fewer, or other steps.Additionally, steps may be performed in any suitable order. As used inthis document, “each” refers to each member of a set or each member of asubset of a set.

Although exemplary embodiments are illustrated in the figures anddescribed below, the principles of the present disclosure may beimplemented using any number of techniques, whether currently known ornot. The present disclosure should in no way be limited to the exemplaryimplementations and techniques illustrated in the drawings and describedabove.

Unless otherwise specifically noted, articles depicted in the drawingsare not necessarily drawn to scale.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the disclosureand the concepts contributed by the inventor to furthering the art, andare construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present disclosurehave been described in detail, it should be understood that variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the disclosure.

Although specific advantages have been enumerated above, variousembodiments may include some, none, or all of the enumerated advantages.Additionally, other technical advantages may become readily apparent toone of ordinary skill in the art after review of the foregoing figuresand description.

To aid the Patent Office and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims or claimelements to invoke 35 U.S.C. § 112(f) unless the words “means for” or“step for” are explicitly used in the particular claim.

What is claimed is:
 1. A system for performing force sensing with ahaptic transducer comprising: a signal generator configured to generatea signal for driving the haptic transducer; and a processing subsystemconfigured to: monitor at least one electrical operating parameter ofthe haptic transducer responsive to the signal; and determine a forceapplied to the haptic transducer based on a variation of the at leastone operating parameter.
 2. The system of claim 1, wherein the signalcomprises a haptic waveform signal.
 3. The system of claim 1, whereinthe force is indicative of force applied to a host device comprising thehaptic transducer by a user of the host device.
 4. The system of claim1, wherein the processing subsystem is further configured to cause anoccurrence of an action in response to determining that force has beenapplied to the haptic transducer.
 5. The system of claim 4, wherein theaction comprises a modification of the signal for driving the haptictransducer.
 6. The system of claim 4, wherein the action comprisesinteraction with a user interface of a host device comprising the haptictransducer.
 7. The system of claim 4, wherein the action comprisesmonitoring a health indicator of a user of a host device comprising thehaptic transducer.
 8. The system of claim 4, wherein the processingsubsystem is further configured to cause the occurrence of the action ifthe variation of at least one operating parameter exceeds a thresholdvariation.
 9. The system of claim 1, wherein the at least one operatingparameter comprises a back electromotive force of the haptic transducer.10. The system of claim 1, wherein the at least one operating parametercomprises a voltage across the haptic transducer.
 11. The system ofclaim 1, wherein the at least one operating parameter comprises acurrent through the haptic transducer.
 12. The system of claim 1,wherein the at least one operating parameter comprises a compleximpedance of the haptic transducer.
 13. The system of claim 1, whereinthe at least one operating parameter comprises a quality factor of thehaptic transducer.
 14. A method for performing force sensing with ahaptic transducer comprising: generating a signal for driving the haptictransducer; monitoring at least one electrical operating parameter ofthe haptic transducer responsive to the signal; and determining a forceapplied to the haptic transducer based on a variation of the at leastone operating parameter.
 15. The method of claim 11, wherein the signalcomprises a haptic waveform signal.
 16. The method of claim 14, whereinthe force is indicative of force applied to a host device comprising thehaptic transducer by a user of the host device.
 17. The method of claim14, further comprising causing an occurrence of an action in response todetermining that force has been applied to the haptic transducer. 18.The method of claim 17, wherein the action comprises a modification ofthe signal for driving the haptic transducer.
 19. The method of claim17, wherein the action comprises interaction with a user interface of ahost device comprising the haptic transducer.
 20. The method of claim17, wherein the action comprises monitoring a health indicator of a userof a host device comprising the haptic transducer.
 21. The method ofclaim 17, further comprising causing the occurrence of the action if thevariation of at least one operating parameter exceeds a thresholdvariation.
 22. The method of claim 14, wherein the at least oneoperating parameter comprises a back electromotive force of the haptictransducer.
 23. The method of claim 14, wherein the at least oneoperating parameter comprises a voltage across the haptic transducer.24. The method of claim 14, wherein the at least one operating parametercomprises a current through the haptic transducer.
 25. The method ofclaim 14, wherein the at least one operating parameter comprises acomplex impedance of the haptic transducer.
 26. The method of claim 14,wherein the at least one operating parameter comprises a quality factorof the haptic transducer.